為什麼number的簡寫會是【no.】???

The word "number" is a general term which refers to a member of a given (possibly ordered) set. The meaning of "number" is often clear from context (i.e., does it refer to a complex number, integer, real number, etc.?). Wherever possible in this work, the word "number" is used to refer to quantities which are integers, and "constant" is reserved for nonintegral numbers which have a fixed value. Because terms such as real number, Bernoulli number, and irrational number are commonly used to refer to nonintegral quantities, however, it is not possible to be entirely consistent in nomenclature.
To indicate a particular numerical label, the abbreviation "no." is sometimes used (deriving from "numero," the ablative case of the Latin "numerus"), as is the less common "nr." The symbol # (known as the octothorpe) is commonly used to denote "number."

2006-12-16 15:18:53 補充：
№，Numero sign（數的符號），Unicode字元0x2116，在俄語書寫表示數。19世紀從法國和德國借用，現時多以「No.」代之。它是拉丁字母N加上上標且有底線的o。http://zh.wikipedia.org/w/index.php?title=№&variant=zh-hk

還有，thank的縮寫為甚麼是ｔｈｘ？